1. Industrial useful field
The present invention relates to a method and apparatus for grinding notches of a disc form workpiece, e.g. a semiconductor silicon wafer. More specifically, the invention relates to a method and apparatus for grinding notches of a semiconductor wafer so as to perform chamfering thereof in a circumferential direction of the notches as well as in the plate thickness direction of the notched semiconductor wafers by moving a rotating grinding wheel in a direction of an axial line (direction X) of the rotary shaft thereof or rotating said wafer around the center axis thereof (direction .theta.), moving the wafer in a direction of approach to or alienation from the wheel (direction Y) and moving said wheel in a direction (direction Z) to cross orthogonally with said directions X and Y.
2. Description of Prior Art
The "semiconductor wafer" as referred to in this invention covers a thin disk of semiconductor material, exemplarily silicon, which is normally obtained by slicing a cylindrical refined single crystal mass, for example, silicon mass as shown in FIG. 6. Its surface is polished into mirror face, on which various semiconductor devices are formed by various etching technics, lithography, etc. A semiconductor wafer is a thin disk having its sizes of, for example, 10-400 mm in diameter, 200 .mu.m-10 mm in thickness. In order to facilitate aligning the circumferential direction, the wafer is provided with an orientation flat (OF) forming a linear portion on a part of its periphery or a nearly V-notch.
On the other hand, during fine machining of the surface of a semiconductor wafer, occurrence of fly dust on the surface or outer periphery of the semiconductor wafer becomes a serious matter of great concern. If a semiconductor wafer has a sharp portion on its outer periphery, a large amount of dust is produced. Accordingly, elimination of sharpness on a boundary face portion between the orientation flat or a notch and an outer pheripheral face, especially extending the plate thickness of the orientation flat or the notch, is an effective means of preventing flying of dust.
To process an orientation flat or a notch in an accurate dimension leads to reduction of labor for location of the workpiece to be machined in the subsequent fine finemachining step. Accordingly, grinding of orientation flat or notch is required to be performed in as high accuracy as possible.
Conventionally, due to the difficulty of removing the sharp edges of the nearly V-notch, an orientation flat which is considered readily machinable has frequently been used. However, the orientation flat has a drawback that it requires a large portion to be cut off in working, so that effective utilization of precious semiconductor wafer is prevented.
As a method of grinding the notch, conventionally chemical polishing or contoured blade has been adopted. The chemical polishing process is, as shown in FIG. 6, to immerse a disk-form semiconductor wafer 2 sliced off from a cylindrical ingot of a semiconductor material, for example silicon 1 in an etching liquid to remove chemically the edge portion 2a having various defects, e.g. processing strain, crystal defect, etc. The said process has defects such that, as shown in FIG. 7, erosion occurs not only in the edge portion 2a but also in the whole area 2b immersed in the etching liquid to become thin, so that the flatness of the wafer is degraded to provide undesirable effect on the fine processing in the next step. Further, the said process has such defect that it is very small amount of processing and allows only insufficient processing to prevent flying of submicron dust which is problematic in processing super LSI and the like.
In the form grinding method, grinding notch 2c may be performed with a cutter having the same shape as the required notch 2c to be chamfered so that the corresponding cutter must be prepared on each occasion where the shape of the notch 2c is changed. Further, as the shape of said cutter changes as the frequency of use of the cutter for grinding increases, the cutter which has been used to some extent requires to be replaced by a new cutter. Thus, the form grinding method has defects in that it is economically expensive, and it requires many steps for the setup work. Further, as it is not possible to carry out chamfering of the edges of the V-notch 2c on the outer periphery 2d of the wafer 2 with a single grinding stone, normally the chamfering in the direction of the plate thickness only is carried out, and fine machining is obliged to carry out in the next step. However, due to the generation of dust from the unprocessed edge portion 2a in the circumferential direction, there has been a defect of having significant adverse effect such as to cause breakage of the lead wire on said wafer.